 Okay, let's try this one. It says calculate the z effective for the following atoms, and then it gives you these atoms sodium potassium silicon and chlorine. So remember z effective is the effective nuclear charge. So the actual amount of charge, positive charge that I'm feeling when I'm outside of the app. So if you recall z, if you recall from a long time ago, I think chapter 2, z is the nuclear charge of the atom itself, okay? And z effective, there's actually a formula that I would hope you would remember, that z effective equals z minus the number of electrons of the, we'll put it this way, the electrons of the noble gas before it, okay? So let's go ahead and look for the nuclear charge of all four of these atoms. So look up at the periodic table, sodium is what? 11, potassium 15, 19, 19, right, I got it right, right? Okay, silicon is 14, 14, and chlorine 17, 17, right? Okay, so what's the noble gas before sodium? Neon, and how many electrons does it have in it? 10, so we're just going to say 11 minus 10 equals, and this will be the z effective, so positive 1. So this one, what's the one before it? It's going to be argon, right? So that's 18 So plus 1, that's much better. This one, of course, is going to be the same as sodium, neon plus 4 will be z effective, and this one, of course, will also be neon, right? So it's going to be minus 10, it's going to be plus 6. Okay, so this z effective kind of helps you identify or kind of think about that periodic trend, about the size of the atoms themselves, so when you increase the z effective, as you go across the period, the atoms get smaller, okay? So if you'll notice, if we wanted to put these in order of biggest to smallest, we'll say sodium, silicon, and chlorine, right, because they're all in the same period, right? You'll see that sodium is the biggest because it's got the least effective nuclear charge and chlorine's the smallest because it's got the most effective nuclear charge. So if we wanted to rank these in order, right? Order decreasing order, we'll say. So that would be from biggest to smallest, and then we'll just look at those three that we were talking about, so we would say sodium is going to be bigger than silicon, which is going to be bigger than chlorine, like that. Are there any questions on that? So that kind of pits up both of those points, I think.